Metal complex catalysts for the hydrogenation of olefins have been disclosed in past years, typically consisting of a transition metal (e.g. Ru, Rh, Os, Ir) which is coordinated with different types of ligands such as phosphine ligands (e.g. PPh3 or PCy3), hydrogen, halides, CO, NO or N-heterocyclic carbenes (NHCs). A typical example for a rhodium-based hydrogenation catalyst is the “Wilkinson catalyst” as shown in formula A.

Among the above mentioned ligands, N-heterocyclic carbene ligands have gained high popularity in organometallic chemistry. Their high sigma donating ability and steric bulk has proven functional in stabilizing low-coordinate transition metal complexes, and the added electron richness they confer a metal center can be advantageous in the activation of π-acidic substrates.
In Lee, H. M., Smith Jr., D. C., He, Z., Stevens, E. D., Yi, C. S., Nolan, S. P. Organometallics, 2001, 20 (4), 794-797 and Beach, N. J., Blacquiere, J. M., Drouin, S. D., Fogg, D. E. Organometallics, 2009, 28 (2), 441-447, synthesized mixed NHC-phosphine variants of the type RuHCl(CO)(PR3)(NHC) as shown in formula B are disclosed. It was found that the use of labile phosphines in combination with strongly donating NHCs had a positive effect on rates of catalysis. The document is silent about the use of these complexes for the hydrogenation of nitrile rubbers.

In Chatwin, S. L., Davidson, M., Doherty, C., Donald, S. M., Jazzar, R., Macgregor, S., McIntyre, G., Mahon, M., Whittlesey, M. Organometallics 2006, 25 (1), 99-11, a metal complex with the formula RuHX(CO)(NHC)2 is described as shown in formula C. Lee, J. P., Ke, Z., Ramírez, M. A., Gunnoe, T. B., Cundari, T. R., Boyle, P. D., Petersen, J. L. Organometallics 2009, 28 (6), 1758-1775 discloses the hydrogenation of 1-hexene with the complex of the formula C. However, the catalytic activity is poor compared to [Ru(IMes)2(CO)(H)][BAr′4]. Furthermore, it is not selective for olefins.

However, more recently a number of novel divalent carbon species have been synthesized based on other heterocycles such as triazole and pyrazole, offering different electronic characteristics to the classic NHC, many of which have been shown to be more strongly sigma donating.
In Lavallo, V., Dyker, C. A., Donnadieu, B., Bertrand, G. Synthesis and Ligand Properties of Stable Five-Membered-Ring Allenes Containing Only Second-Row Elements. Angew. Chem. Int. Ed. 2008, 47, 5411-5414, the synthesis of stable pyrazolin-4-ylidenes that featured heteroatoms at the 3,5 positions of the ring (page 5412, structure 3b), termed “cyclic bent allenes” (CBAs), are reported. It has been shown computationally and experimentally that the introduction of these heteroatoms has a strong influence on the electronic nature of the system, as the ring π-electrons are exocyclically delocalized through these positions. This localizes two lone pairs of electrons on the central carbon atom, making the ligands electronically analogous to carbodicarbenes, part of a growing family of carbon(0) compounds. The isolation of a Rh-biscarbonyl complex as shown in formula D (page 5413, structure 4) bearing this ligand revealed their greater donating power relative to NHCs. However, no mixed CBA/NHC complexes are disclosed. Furthermore, the document is silent about the use of the complex for the hydrogenation of unsaturated olefins.

In Pranckevicius, C., Stephan, D. W. Three-coordinate, Cyclic Bent Allene Iron Complexes. Organometallics, 2013, 32, 2693-2697, the preparation of a novel Fe(CBA) complexes as shown in formula E is disclosed. However, the document is silent about the use of these complexes as catalysts for the hydrogenation of olefins.

In DeHope, A., Donnadieu, B., Bertrand, G. Grubbs and Hoveyda-type ruthenium complexes bearing a cyclic bent-allene. Journal of Organometallic Chemistry, 2011, 696, 2899-2903, a ruthenium-based cyclic bent allene complex is disclosed as shown in formula F (page 2900, complex 3). However, the document discloses only Grubbs and Hoveyda-type ruthenium complexes and is totally silent about the use of these complexes as catalysts for the hydrogenation of unsaturated olefins.

In WO 2009/089483, bent allene metal complexes are disclosed. According to paragraph [0052], the bent allene can be a 5-membered heterocyclic ring. In paragraph [0057], it is disclosed, that the metal of the bent allene metal complex might be inter alia ruthenium. In paragraph [0060], it is disclosed, that anionic ligands, preferably halides, are suitable as anionic ligands. Hydride as a ligand for the metal complexes is not disclosed in the document. Other suitable ligands can be carbene ligands such as the diaminocarbene ligands (e.g., NHCs). However, paragraph [0060] discloses also the use of phosphines as neutral ligands.
The document discloses in paragraph [0063] the use of bent allene metal complexes as catalysts for a variety of synthetic organic reaction, including amine arylation, Suzuki coupling reactions (aryl-aryl or aryl-alkyl coupling reactions), and α-arylation reactions, hydroformylation (of alkenes and alkynes), hydrosylilation (of alkenes, alkynes, ketones and aldehydes), ring-closing metathesis (RC), ring-opening polymerization metathesis (ROMP), cross metathesis (CM), self-metathesis, acyclic diene metathesis polymerization, ene-yne metathesis, carbonylation, hydroarylation and hydroamination. However, the document is totally silent about the use of these bent allene metal complexes as catalysts for hydrogenation reaction of unsaturated compounds.
The object of the present invention was thus to provide a stable catalyst with excellent activity for the hydrogenation of olefinic compounds, preferable for unsaturated polymers, more preferable for unsaturated nitrile rubbers.